1. Field of the Invention
This invention relates to an electric motor, and, more particularly, it is concerned with the d.c. electric motor of a flattened shape, wherein a rotary armature including a coil assembly formed of a combination of at least two disc-shaped coils, each having radial segments, is disposed within the field of a fixed field permanent magnet, and, at the same time, brushes are in contact with an area of a cylindrical commutator electrically connected with the coil assembly and fixedly provided on the rotary shaft, at which the fixed field permanent magnet overlaps.
2. Description of the Prior Art
Increasing tendency of tape recorders and other acoustic devices toward smaller sizes has given rise to the need for smaller electric motors to be used therewith. Reduction in size of such motors may be realized either diametrally or axially thereof. In a micro-cassette tape recorder or the like, for example, flattening of the motor and making the direction of peripheral rotation of the rotary shaft coincident with the direction of tape running would be more advantageous in terms of the drive transmission mechanism.
For this reason, a number of motors of an axially flattened type have heretofore been proposed for use with tape recorders and other acoustic devices, among which there are such ones having the armature coils formed in a disc-shape to flatten the motors to the axial direction thereof. However, in the conventional electric motors of this type, a cylindrical commutator is provided on the very same rotary shaft having the disc-shaped coils disposed thereon, and, since such commutator is laterally projected with respect to the fixed fields lying on the opposite sides of the disc-shaped coils, the motor should be thicker in axial direction thereof for the projected part, so that it can be said to be the realization of the ideal flattened electric motor. To overcome the drawbacks involved in the use of such cylindrical commutator, there have also been proposed electric motors, in which the cylindrical commutator is replaced by a disc-shaped commutator. On the other hand, in a disc-shaped armature having disc-shaped coils, the radial segments of the coils produce rotational force, owing to which mere provision of a disc-shaped commutator would pose a problem such that it restricts the length of the radial segments of the coils and thus reduces the power of the motor.